Perhaps not what you think of as "art" but useful for teaching
techiques of graphic manipulation in photoshop or photopaint is a
project I do every year. It involves having the students create
one of those "find the seven changes" type pictures. I have them
go on the web and find a decent-sized picture which would be good
to have changes (sporting events and crowd scenes seem to be
best). Students make two copies, and on one they use the various
tools to make changes to one of the photos -- subtle and not so
subtle. I've had students do things like change the colour of a
stripe on a jersey, cut and paste the name from one player to
another, change the logos on opposing teams, erase people in the
audience, insert famous faces in the audience, etc. etc.. For the
finished product, they put both photos on one page in a
wordprocessing program with the instructions to find however many
changes they made. On another page they type the answers. They
then mount them so the answers are 'on the back'. These are great
things to display on a hallway bulletin board ... they're good
things to have in the hallways to occupy parents' time during
open house night or parent interview night.